.parent{
    width: 150px;
    height: 150px;
    background-color:tomato;
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
}
.child{
    width: 100px;
    height: 100px;
    background-color:springgreen;
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
}